Process for improved meta-xylene yield from C8 aromatics

Abstract

Meta-xylene is recovered from admixture with other C 8 aromatic hydrocarbons including ortho-xylene by liquid phase adsorptive separation. Performance is improved by reducing the concentration of ortho-xylene through adding a sidecut to a prefractionator preparing the feedstock to adsorptive separation.

1. A process for recovering high-purity meta-xylene from a feedstock comprising C 8  and heavier aromatic hydrocarbons which comprises:
 (a) distilling the feedstock to separate C 8  aromatic hydrocarbons from heavier hydrocarbons in a xylene column which comprises a sidecut for obtaining an ortho-xylene concentrate; 
 (b) contacting the C 8  aromatic hydrocarbons in a selective-adsorption step at liquid-phase adsorption conditions with an adsorbent comprising a zeolite, adsorbing the meta-xylene, removing the nonadsorbed portion of said mixture from contact with said adsorbent by means of a raffinate stream and recovering the high-purity meta-xylene by desorption with a desorbent at desorption conditions. 
 
     
     
       2. The process of  claim 1  wherein the ortho-xylene concentrate comprises at least about 40 wt-% ortho-xylene. 
     
     
       3. The process of  claim 1  further comprising fractionation of the ortho-xylene concentrate to recover high-purity ortho-xylene. 
     
     
       4. The process of  claim 1  wherein the adsorbent comprises Y-zeolite. 
     
     
       5. The process of  claim 1  wherein the desorbent consists essentially of toluene. 
     
     
       6. The process of  claim 1  wherein the desorbent consists essentially of indane. 
     
     
       7. The process of  claim 1  wherein the adsorption conditions include a temperature of from 100 to 150° C. 
     
     
       8. The process of  claim 1  further comprising recovering paraxylene from the feedstock. 
     
     
       9. The process of  claim 1  wherein the feedstock has been prepared by extraction of aromatics from a hydrocarbon mixture. 
     
     
       10. A process for recovering high-purity meta-xylene from a feedstock comprising C 8  and heavier aromatic hydrocarbons which comprises:
 (a) distilling the feedstock to separate C 8  aromatic hydrocarbons from heavier hydrocarbons in a xylene column which comprises a sidecut for obtaining an ortho-xylene concentrate; 
 (b) contacting the C 8  aromatic hydrocarbons in a selective-adsorption step at liquid-phase adsorption conditions with an adsorbent comprising a zeolite, adsorbing the meta-xylene, removing the nonadsorbed portion of said mixture from contact with said adsorbent by means of a raffinate stream and recovering the high-purity meta-xylene by desorption with a desorbent at desorption conditions; and, 
 (c) isomerizing the raffinate stream with an isomerization catalyst at isomerization conditions to obtain an isomerized stream and distilling the isomerized stream along with the feedstock to separate C 8  aromatic hydrocarbons from the heavier hydrocarbons and an ortho-xylene concentrate. 
 
     
     
       11. The process of  claim 10  wherein the ortho-xylene concentrate comprises at least about 40 wt-% ortho-xylene. 
     
     
       12. The process of  claim 10  further comprising fractionation of the ortho-xylene concentrate to recover high-purity ortho-xylene. 
     
     
       13. The process of  claim 10  wherein the adsorbent comprises Y-zeolite. 
     
     
       14. The process of  claim 10  wherein the desorbent consists essentially of toluene. 
     
     
       15. The process of  claim 10  wherein the desorbent consists essentially of indane. 
     
     
       16. The process of  claim 10  wherein the adsorption conditions include a temperature of from 100 to 150° C. 
     
     
       17. The process of  claim 10  further comprising recovering paraxylene from the feedstock. 
     
     
       18. The process of  claim 10  wherein the feedstock has been prepared by extraction of aromatics from a hydrocarbon mixture. 
     
     
       19. The process of  claim 10  wherein the feedstock is unextracted. 
     
     
       20. The process of  claim 1  wherein the feedstock is unextracted.